Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment, as examples. Semiconductor devices are typically fabricated by sequentially depositing insulating or dielectric layers, conductive layers, and semiconductive layers of material over a semiconductor substrate, and patterning the various material layers using lithography to form circuit components and elements thereon. Dozens or hundreds of integrated circuits are typically manufactured on a single semiconductor wafer. The individual dies are singulated by sawing the integrated circuits along scribe lines on the wafer. The dies may be packaged separately, in multi-chip modules, or in other types of packaging. As semiconductor devices have decreased in size, smaller packages such as wafer level packaging (WLP) have begun to be developed, in which integrated circuits (ICs) are placed on a carrier having wiring for making connection to the ICs and other electrical components. To further increase circuit density, three-dimensional (3D) ICs have also been developed, in which two or more dies or ICs are bonded together and electrical connections are formed between the dies and contact pads on an interposer, which is attached to a substrate.
Wiring of semiconductor devices is typically formed in back-end-of the line (BEOL) processes. Multiple layers of conductive material are used to form wiring and other conductive structures such as capacitors and inductors in some applications. Resistance-capacitance (RC) time constant, RC delay characteristics, and resistance of conductive wiring and conductive structures are concerns in many semiconductor devices, particularly as devices are decreased in size.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of some of the embodiments and are not necessarily drawn to scale.